Process for the production of photographic images

ABSTRACT

THE INVENTION RELATES TO A PROCESS FORTHE PRODUCTION OF PHOTOGRAPHIC IMAGES, IN PARTICULAR A COPYING PROCESS, WHEREIN A SUPPORTED LAYER WHICH CONTAINS IMAGEWISELY DISTRIBUTED DEVELOPMENT NUCLEI FOR DISSOLVED SILVER SALTS, IN EITHER VISIBLE OR INVISIBLE FORM, IS DEVELOPED IN THE PRESENCE OF AN AQUEOUS SOLUTION OF SILVER SALTS SOLUBLE IN WATER AT PH VALUES BETWEEN 1 AND 7.

United States Patent Olhce 3,554,750 Patented Jan. 12, 1971 A 49,25 Int. Cl. G03c 1/06, 5/54 US. Cl. 9629 17 Claims ABSTRACT OF THE DISCLOSURE The invention relates to a process for the production of photographic images, in particular a copying process, wherein a supported layer which contains imagewisely distributed development nuclei for dissolved silver salts, in either visible or invisible form, is developed in the presence of an aqueous solution of silver salts soluble in water at pH values between 1 and 7.

This application is a continuation-in-part of the copending application Ser. No. 549,191, filed May 11, 1966, now abandoned.

In the conventional copying processes, a light-sensitive silver halide emulsion layer is exposed to light through an original and then developed in an alkaline medium and fixed in the usual manner.

It is practically impossible to process the usual silver halide emulsion layers in acid developer solutions after exposure because only a weak silver image is formed after a very long development time. For many reasons it is desirable to avoid the usual alkaline development baths. The disadvantages of alkaline developers are, for example, relatively long processing times due to the necessary Washing out, the risk of yellowing of the final image due to residues of alkali, or damage to the skin in the alkaline baths.

It is an object of the invention to develop processes for the production of photographic images, in particular copying processes, in which alkaline developing baths are avoided.

- We now have found that supported layers which contain in imagewise distribution development nuclei for silver salts, for example a latent image in a visible or invisible form, are developed into visible images at pH values between 1 and 7, if during the development they are in effective contact with an aqueous solution of silver salts having a solubility in water at a pH between 1 and 7 of at least 0.2 g./l. silver. The layer containing the development nuclei distributed according to the image, will hereinafter be termed the imagewise nucleated layer.

A very wide variety of imagewise nucleated layers can be used for the process according to the invention. The only condition to be fulfilled is that the said layer contains nuclei at which the soluble silver salts 'can be reduced. Thus, for example, it is possible to use layers which contain a photographic silver image or an image of other finely divided metals, for instance, of gold or of heavy metal sulfides, such as silver sulfide, nickel sulfide or the like.

According to a preferred embodiment exposed there is used as imagewise nucleated layer, a silver halide emulsion layer which contains development nuclei in the form of latent image specks produced on exposure. Light-sensitive silver halide emulsion layers such as silver chloride, chlorobromide or bromide layers, which may have a silver iodide content of up to 30 mols percent, preferably up to about 10 mols percent, are for example suitable for this purpose. Conventional silver halide emulsion layers contain between 1l0 g. silver/m. in the form of silver halide. Particularly suitable are silver halide emulsion layers which have only a relatively small concentration of silver halide of about 0.01 to 1.5 g., preferably 0.1 to 1.0 g., silver per square meter. Layers of the kind can be produced in the usual manner, for example, by diluting silver halide gelatin emulsions of common concentration with a hydrophilic binding agent, for example, with alginic acid or its derivatives such as salts, in particular alkali metal salts, esters, in particular with aliphatic alcohols of up to 5 carbon atoms, or amides, or starch ethers, polyvinyl alcohol, polyvinylpyrrolidone, cellulose derivatives such as methyl cellulose, carboxymethyl cellulose, hydroxyethylcellulose or the like, or gelatin or other proteins such as casein, albumin or zein. It is also possible to precipitate the silver halide in a diluted low concentration. The preparation of such emulsions is described, for example, in British patent specification 920,277.

The light-sensitive layers can be chemically or optically sensitized in the usual manner. For optical sensitization, there may be used any dyes suitable for silver halide, e.g., any polymethine dyes such as carbocyanines, merocyanines, betaine cyanines and styryl dyes.

In addition, the usual stabilizers may be added. For example, heterocyclic mercapto compounds, such as lphenylmercaptotetrazoles, 1-phenyl-3-mercapto-triazole-l, 2,4 or azaindenes as described in the article by Birr in Z. wiss, pnot, vol. 47 (1952), pp. 2-8.

The process of the invention includes the essential steps of placing the imagewise nucleated layer, preferably an exposed silver halide emulsion layer containing an extremely low amount of silver halide, in contact with an aqueous solution of a soluble silver salt and developing at a pH between 1 and 7.

The soluble silver salt can be provided by placing the imagewise nucleated layer into contact with a layer containing the soluble silver salt from which the silver salt is dissolved in the presence of water or by treating the imagewise nucleated layer directly with an aqueous solution of the silver salt. In the first mentioned embodiment the soluble silver salt-containing layer can be applied either underneath or above the imagewise nucleated layer on the same support or on a separate support. The last mentioned arrangement is preferred since in that case it is possible to obtain a negative silver image in the silver halide layer and, after final processing, a direct positive silver image in the layer containing the soluble silver salts.

If the silver salts which are soluble at a pH between 1 and 7 are arranged in a separate layer, the usual photographic types of gelatin can be used as binders for these layers. The gelatin may, however, be partly or completely replaced by other proteins, such as casein, albumin, zein, or by alginic acid or its derivatives such as salts, esters in particular with aliphatc alcohols of up to 5 C-atoms, or amides, or starch ethers, polyvinyl alcohol, polyvinyl acetate, polyvinylpyrrolidone, cellulose derivatives such as methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose or the like. The application of silver in these layers is about 0.1 to 2.5 g./m. preferably 0.5 to 1.5 g./m. in the form of the soluble silver salt. When the imagewise nucleated layer while contacting the layer containing the soluble silver salts is treated with an aqueous bath in the presence of developers, the soluble silver salt is partly dissolved and diffusesinto the imagewise nucleated layer. At those portions where development nuclei are present, the silver salt which has diffused over is reduced so that in that region a concentration gradient is established which considerably accelerates the dissolution of the silver salts in the layer which contains the silver salts. At those portions of the imagewise nucleated layer, where no development nuclei are present, this effect does not occur and the soluble silver salts substantially remain undissolved in the said layer. In this way, the layer with the soluble silver salts is dilferentiated according to the image. The resulting silver salt image in the said layer is negative to the image of developed silver in the layer which contain in imagewise distribution the development nuclei.

The silver salt image can subsequently be made visible by uniform exposure and development or by chemical reduction. According to another embodiment silver salt layers of particular composition can be applied so that a silver image is immediately formed in the said layer.

According to another embodiment of the process, development nuclei of the kind described hereinbefore are uniformly added to the layer containing the soluble silver salts. With these uniformly nucleated layers an immediately visible silver image is formed in that layer upon development. That silver image is negative with respect to that formed in the imagewise nucleated layer. The concentration of the nuclei is critical. If the concentration is too high, the soluble silver salts of the layer will be reduced before they have a chance to diffuse into the imagewise nucleated layer. If the concentration of the nuclei is insufficient, the result is an unsatisfactory formation of silver. The optimum concentration depends somewhat on the kind of the imagewise nucleated layer, the type of acid soluble silver salts and in particular the binder used for both layers. In general, a concentration of development nuclei corresponding to a silver nuclei concentration of about 1 to 150 mg. per m? of the layer containing the soluble silver salt is sufiicient.

of inorganic or organic cellulose esters or polyesters, in

particular polyethylene glycol terephthalate, the layer containing the soluble silver salt. That layer is not removable in warm water. The silver salt layer is overcoated by the imagewise nucleated layer, for example, a silver halide layer which contains a binding agent that can be washed off with warm water, for example, unhardened gelatin or carboxymethyl cellulose. After exposure and imagewise formation of development nuclei in the upper layer, the material is developed and the imagewise nucleated layer is subsequently washed off in warm water, while the layer which contained the soluble silver salts and which after processing contains a silver image remains adhered on the support.

As pointed out hereinbefore, it is advantageous to form two photographic images, a visible silver image in the imagewise nucleated layer in accordance with the development nuclei and a silver image in the soluble silver salt-containing layer upon development or reduca tion of the remaining silver salt, which latter image is, negative with respect to the silver image in the imagewise nucleated layer. Since the process of the invention proceeds fairly rapidly, it is advantageous to carry out the processing in apparatus such as those used, for example, for the silver salt diffusion process.

If the soluble silver salts are provided in the form of an acid aqueous treating solution, the imagewise nucleated layer may either be initially treated with the solution and then in the developing bath or alternatively it may be initially treated with the developer solution and then with the silver salt solution. The silver is then deposited at the development nuclei, for example, the latent image specks formed by exposure, in the silver halide emulsion layer. An excellent silver image is formed with outstanding reproduction of the grey tone-values. How the process is carried out in detail will depend primarily upon the arrangement of the developer which may either be present in the imagewise nucleated layer or alternatively may be used in the form of an aqueous solution. In the former case, the imagewise nucleated layer may be simply treated with water and then with an aqueous solution of the silver salts, or directly with an aqueous solution of the silver salts. In the latter case it is advantageous initially to treat the imagewise nucleated layer with an aqueous solution of the developer and then with an aqueous solution of the silver salts. It is not advisable to use the silver salts and the developer substances in a common solution because solutions of this kind are not sufficiently stable on storage. Reduction of the silver salts in such solution can only be avoided with difficulty.

The aqueous solution of the silver salts which have a pH between 1 and 7 should contain at least 0.2 g./l. silver in the form of the soluble silver salt. There is no upper limit of the concentration, so that saturated solutions of the silver salts can be used. Preferred are solutions which contain between 0.7 and about 4 g./l. silver in the form of the soluble silver salt.

Instead of treating the exposed silver halide layers with aqueous solutions, they can also be treated with pastes in which the developer substances or the silver salts are present. Pastes of this kind are obtained by adding a thickener as known per se to the aforementioned solutions, as known per se, such as derivatives of alginic acid, for instance sodium alginate, or alginic acid esters, polyvinyl alcohol or carboxyalkyl cellulose, for instance carboxymethyl cellulose.

Suitable developers for the process according to the present invention include all developers capable of reducing the soluble silver salts under the processing conditions at acid or neutral pH-values. The following developers, for example, may be used: developers of the 3-pyrazolidone series, preferably 1-phenyl-3-pyrazolidone or its derivatives as well as 3-aminopyrazolines, for example, 1-paminophenyl-3-aminopyrazoline or its derivatives as described, for example, in British patent specification 768,- 071; 4-aminopyrazolones or its derivatives as described, for example, in British patent specification 768,071, for example, 1-phenyl-3-carbonamido-4-amino-5-pyrazolone and l-phenyl-3-methyl-4-amino-S-pyrazolone; hydroxytetronic acid or its derivatives such as ascorbic acid or similar products or salts of reducing heavy metals such as ferrous salts, for example ferrous citrate. The first-mentioned developers are particularly suitable.

The following developers of the 3-pyrazolidone series exhibit particular utility: l-phenyl-3-pyrazolidone; 1-mtoluyl-3-pyrazolidone; l-p-toluyl-3-pyrazolidone; l-phenyl- 4-methylpyrazolidone; 1-phenyl-5-methyl-3-pyrazolidone; 1,4-dimethyl-3-pyrazolidone; 4-methyl-3-pyrazolidone; 4, 4-dimethyl-3-pyrazolidone; 1-phenyl-2-acetyl-3-pyraz0lidone; 1-phenyl 4,4-dimethyl-3-pyrazolidone; l-(4-bromophenyl) -3 -pyrazolidone.

The aforementioned developers may be used in combination with one another or with other known developers.

The developers may be used in the form of aqueous solutions of pH 1 to 7 or alternatively they may be added to the imagewise nucleated layer in which case they are used in quantities of preferably 0.01 to 2.5 g. per square meter. Aqueous solutions suitable for development preferably contain between 0.1 and 50 g., particularly 0.5 to 20 g., of developer per liter.

For adjusting to a pH below 7, the acids to be used must not form a silver salt which is less soluble than the we acid-soluble silver salts used. Consequently, hydrohalic' acids, for example, cannot be used. Examples of suitable acids are inorganic acids such as sulfuric acid and nitric acid and organic acids in particular aliphatic carboxylic acids having up to 6 carbon atoms such as acetic acid, citric acid, adipic acid and thelike, and acids the silver salts of which are used in the process according to the invention. The acids can also be added either to the imagewise nucleated layer, for instance the silver halide emulsion layer or to the layer which contains the acid soluble silver salt or to the developer. In cases where acidcontaining emulsion layers are used, the acids are added in quantities of between 0.001 and 10 g., preferably between 0.1 and 3 g. per square meter depending on the wherein:

n=1 or 2.

R=alkyl, preferably with up to 3 carbon atoms, aralkyl such as benzyl or phenylethyl, aryl such as phenyl or naphthyl, or heterocyclic rings such as diazolyl, oxazolyl, triazolyl, oxadia zolyl, thiadiazolyl, tetrazolyl, azaindenyl, preferably tetraor penta-azaindenyl, benzthiazolyl, naphthiazolyl, benzooxazolyl, naphthoxazolyl, pyridyl, quinolyl, pyrimidinyl, quinoxalinyl, quinazolinyl, which radicals may in turn be substituted, for example, by alkyl, alkenyl, preferably with up to 6 carbon atoms, aryl such as phenyl or naphthyl, hydroxyl, alkoxy, aroxy such as phenoxy, acyl preferably acetyl, amino, alkylamino, the alkyl groups of which having up to 5 carbon atoms, acylamino, aryl-substituted amino preferably a phenylamino, mercapto groups substituted with alkyl having up to 6 carbon atoms, a phenyl a naphthyl or a heterocyclic radical, halogen such as chlorine or bromine, sulfo groups carboxyl groups or nitro and the like. The groups R can be substituted by at least one further grouping X=a branched or unbranched alkylene chain having preferably up to 4 carbon atoms, whereby the alkylene chains can further be substituted with aryl preferably a phenyl, hydroxyl, alkoxy, halogen such as chlorine or bromine and the like.

Aliphatic carboxylic acids, the aliphatic chain or which is substituted with an organic thioether grouping, include the following:

1 S-CHz-C O OH Beilstein V013, page 249.

2 L O-(CH2CHz-S'CHz-COOH)2 44.

3 HO 0 C--OHzS-(CH2)a-SCH2-C O OH Beilsteiu, Vol. 3, 3d Supp. Vol.

Part 1, page 417.

4 HO 0 C-CHz-S-CHz-C O OH Beilstein, V01. 3, page 253.

O O OH 5 CH JH OH2C 0 0H Beilstein, Vol.3, page 291.

6 S -CHC O OH Beilstein, Vol. 3, page 291.

S C HO 0.0 H

0 H 7 S-(lH-C O OH Beilstein, Vol. 3, 3d Supp. Vol,

part 1, page 511. 2 2 on-o ooH 2.... Y 8 HOOCCH-(NH )CH2-SCH;COOH J. Am. Chem. 800., Vol.66,

page 1,758 (1944).

O 0 O H Beilstein, Vol. 3, 3d Supp. Vol.

part 2, page 924.

C O OH O 0 OH O 0 0H 10 CH3 v( 3H; Beilstein, Vol. 3, page 439.

OHSS( JH c0011 (10011 11 CHz-C 00H Beilstein, V01. 12, page 485,

TABLECont1nued 26... H0 8 -I| I 1 i 296 C. (decomposition).

N/SCH2C OH-2H2O 27 N-N A BeiisteimgVol. 27, 1st Supp. Vo1.,

s S CHr-COQH pagefil nooo-mosqa s2 150 C" H C-SC 3 S SCHz-COOH CH3 T v Uncrystallized: 1193-8 sonz-ooon I i v I 260 C. (decomposition). H NG k p -s onrcoon v.

' i? 158C 36. -c

, I s S CHa -COOH 31 NI| I 177C n e-o GH2 COOH AH -CH=QH 1 38.. I i V 122.123

l v S-CH2-CHz-COOH a9 CH2-N v v C-S-CHzCOOH 184 C.

CH2 I]I W Particularly suitable are the silver salts of carboxyfurther substituents on the R and X portions selected in acmethylthiomalic acid, S-phenyl-thioglycollic acid, S-triacordance with the general definition as set out above. zolyl-thioglycollic and S-thiadiozolyl-(Z, or 5-)th1'ogly- The compounds may be prepared by the processes collie acid, bis-(beta carboxymethyl thim ethyl ether, and described in the publications referred to in the table. The

substitution products in which these compounds have 75 remaining compounds may be prepared from the corresponding mercaptans and organic halogen compounds or halogen carboxylic acids in alkaline solution by processes similar to those described in Houben-Weyl, vol. 9, PP. 103-113. The compounds can be isolated in the form of free acids or as alkali metal salts. The compounds can be purified by recrystallization from or by solution and reprecipitation from water or alcohol.

The process according to the invention is characterized by the excellent quality of the images obtained. This is partly due to the fact that the silver is deposited in a particularly fine form which yields excellent grey tones.

EXAMPLE 1 A silver halide emulsion layer of low silver content is prepared as follows:

A conventional silver bromide gelatin emulsion is diluted with an aqueous gelatin solution.

A layer of the above emulsion is applied onto a paper support and dried. The final layer had a silver concentra tion of 0.1 g. Ag per m. in the form of silver bromide.

Layer-containing soluble silver salt 33 g. of carboxymethylthiomalic acid (compound 9) are added in the form of a 10% aqueous solution to 1 liter of a 6% aqueous gelatin solution. The solution is acidified with ml. of a aqueous sulfuric acid, and the silver salt is then precipitated at 40 C. by the addition of 18.6 g. of silver nitrate in the form of a 10% aqueous solution. In addition, an aqueous colloidal solution of silver is added, so that the final material contains 0.05 g. of silver nuclei per square meter.

A paper support is coated in the usual manner with the above mixture to which has been added 5 cc. of a aqueous saponin solution and 5 cc. of a formaldehyde solution. The completed, swelled layer has a thickness of about 10 The silver content is about 0.5 g./m. in the form of the silver salt.

Instead of the carboxymethyl thiomalic acid, the following compounds may be used in the given quantities:

s-Phenylthioglycolic acid (compound 4) 20.2 s- [4-amino-6-hydroxypyrimidinyl- (2) ]thioglycolic acid (compound 22) 24.3 s- [4-allyl-5-rnethyl- 1,2,4-triazolyl- 3 ]thioglycolic acid (compound 37) 27 s- [4-aminophenyl-( 1) -;B-thiopropionic acid (compound 38) 23.8

The thioglycolic acid derivatives may be added in the solid form to the hinder or in the form of a 5 to 10% aqueous solution, if necessary with the addition of the quantity of alkali required for dissolving the acids, e.g. aqueous sodium hydroxide.

Processing The silver halide emulsion layer which has been exposed to form a latent image is passed through a 0.5% aqueous solution of 1-phenylpyrazolidone-(3) and then brought into intimate contact with the dry layer containing the soluble silver salts. In the silver halide layer, a silver image is formed at the exposed areas by the reduction of the silver salt that has diffused over at the development nuclei of the latent image. In the soluble silver salt layer an excellent silver image is formed, which is negative in relation to the silver image in the emulsion layer.

EXAMPLE 2 A silver halide layer of low silver content is prepared as follows:

To 1 liter of a 6% gelatin solution are added at 40 C. 1 cc. of a 1% aqueous sodium chloride solution, 3 cc. of a 1% aqueous silver nitrate solution and 1 cc. of a 0.01% aqueous eosin solution. To the completed casting solution there are subsequently added 10 cc. of a 20% aqueous citric acid solution, 20 g. of 1-phenyl-pyrazolidone-(3) 12. dissolved in water, 5 cc. of a 30% aqueous saponin solution and 1.5 cc. of a 40% formaldehyde solution.

The resulting emulsion is cast onto a paper support in the usual manner. The final layer contains per m?, 0.1 g. of silver in the form of silver chloride.

Layer containing soluble silver salt To 1 l. of a 7% aqueous gelatin solution are added 10.5 g. of secondary sodium phosphate of the formula and 5 g. of silver nitrate, both in the form of a 10% aqueous solution. Before casting, 5 cc. of a 40% aqueous formaldehyde solution, 10 cc. of a 30% aqueous saponin solution 15 cc. of aqueous sulfuric acid and 0.03 g. of colloidally divided silver are added per liter.

The emulsion is applied in known manner onto a paper support so that the final layer contains about 0.8 g. of silver per In. in the form of silver phosphate.

Processing The exposed silver halide emulsion layer is moistened with water and brought into close contact with the dry silver phosphate containing layer. After a few seconds, the two layers are separated from each other. In the silver halide emulsion layer is obtained an excellent silver image, and in the layer that contained the silver phosphate a negative image which has excellent contrast and outstanding grey tones.

EXAMPLE 3 To 1 liter of a 6% aqueous gelatin solution are added 33 g. of carboxymethylthiomalic acid (compound 9), 10 cc. of a 20% citric acid solution and 18.6 g. of silver nitrate in the form of a 10% aqueous solution at 40 C. The silver salt of the carboxymethyl thiomalic acid precipitates.

To 1 liter of the solution ready for casting there are added 0.05 g. of colloidal nickel sulfide and 8 cc. of a 40% aqueous formaldehyde solution. The solution is applied in the usual manner onto a baryta-coated paper support. The final layer contains 1 g. of silver in the form of silver salt per rn.

An ordinary silver bromide gelatin emulsion having a silver iodide content of about 5% and containing 0.15 mol silver halide per liter is diluted in the ratio of 1:6 with a 2.5% aqueous solution of carboxymethylcellulose.

This emulsion is applied over the layer of silver salt described above so that the silver halide content in the emulsion layer is about 0.3 g. silver per m.

Processing The above material is exposed through a continuous tone original and developed with a 0.5% aqueous solution of 1 phenyl pyrazolidone (3) to which 30 cc. of a 10% aqueous sulfuric acid had been added per liter. The uppermost silver halide layer is then washed off with water at about 50 C.

In the residual silver salt layer, a silver image with excellent grey tones which is positive with respect to the original is obtained. The following soluble silver salts may be used in the given quantities instead of the carboxymethylthiomalic acid:

s [4,5 dimethyl 1,2,4 triazolyl (3)] thioglycollic acid (compound 27) 22.6

s [1,2,4 triazolyl (2)] thioglycollic acid (compound 29) 19.2

The thioglycollic acid derivative may be added to the binding agent either in the solid form or in the form of a 5-10% aqueous solution, if necessary with addition of the quantity of alkali, e.g., sodium hydroxide, necessary to bring them into solution.

EXAMPLE 4 A silver halide, emulsion layer is produced as follows:

To 1 liter of a 6 .5% gelatin solution are added at 55 C., 120 ml. of a 50% silver nitrate solution and 135 n11. of a 3 N-sodium chloride solution in the presence of ml. citric acid.

To the resulting solution are further added before casting: 2 ml. of a 1% alcoholic solution of 1-phenyl-5-mercaptotetrazole, 5 ml. of a saponin solution and 0.5 m1. of aqueous Formalin The resulting mixture is applied in the usual manner to a paper support to yield a layer which contains 1.5 g. of Ag/m. in the form of silver chloride.

Processing is carried out as in Example 1 with the soluble silver salt-containing layer of Example 1-.

After separation of the two layers, a positive image of the original is obtained in the soluble silver salt-containing layer and a negative silver image of the original in the silver halide layer. Both images are stabilized in the usual manner by fixing and washing with water.

EXAMPLE 5 Processing A photographic material consisting of a gelatin layer bearing a negative silver image on a transparent support of cellulose triacetate is passed through a 0.5% aqueous solution of l-phenylpyrazolidone-(3) and brought into close contact with the soluble silver salt-containing layer described in Example 1. After a few seconds, the two lay ers are separated. A silver image which is negative with respect to the silver image of the above photographic material is obtained in the silver salt-containing layer and is stabilized in the usual manner by fixing and washing with water. The negative original is cleaned by fixing and washing with water.

EXAMPLE 6 An imagewise exposed silver bromide gelatin emulsion layer on a support with a silver coating of 0.1 g./m. in the form of silver bromide and a l-phenyl-3-pyrazolidone content of 1 g./m. is bathed for 40 seconds in a solution of 67.5 g. of carboxymethylthiomalic acid (compound 9) and 32.5 g. of silver nitrate in 1 liter of water, which had been adjusted to pH 1 with sulfuric acid, and then fixed and rinsed with water in the usual way.

An excellent silver image is formed. The final silver image essentially consists of silver from the silver salt of carboxymethyl thiomalic acid.

EXAMPLE 7 An imagewise exposed silver chloride gelatin emulsion layer on a paper support, with a silver coating of 0.1 g./ m? in the form of silver chloride and a l-phenyl-3-pyrazolidone content of 0.7 g./m. is coated with a paste of the following composition which is removed in a fixing bath after a contact time of 20 seconds. The material thus treated is then rinsed with water.

The paste has the following composition:

120 g. of polyvinyl alcohol dissolved in 500 ml. of water,

33.7 g. of carboxymethyl thiomalic acid (compound 9),

and

16.3 g. of silver nitrate dissolved in 450 ml. of water.

The polyvinyl alcohol solution is stirred with the mixture of carboxymethylthiomalic acid and the silver nitrate. The pH of the paste is adjusted to 1 by adding sulfuric acid. Cellulose derivatives such as methyl cellulose can be used instead of polyvinyl alcohol.

Copies of outstanding contrast are obtained.

EXAMPLE 8 An imagewise exposed silver bromide gelatin emulsion layer on a paper support having the composition indicated in Example 1, is bathed for 60 seconds in the following solution and then fixed and rinsed with water in the usual way:

G. s [4,5 dimethyl-1,2,4-triazolyl-3(3)]-thioglycolic acid (compound 27) 12.5 Silver nitrate dissolved in 1 liter of water 10 The pH of the solution is adjusted to 2 with sulfuric acid. An excellent silver image of the original is obtained.

EXAMPLE 9 An imagewise exposed silver bromide gelatin emulsion layer on a paper support with a silver content of 2.5 g./m. in the form of silver bromide is bathed in the soluble silver salt solution described in Example 8, developed for 60 seconds in an aqueous solution of 5 g./l. of 1- phenyl-3-pyrazolidone, and then fixed and rinsed with water in the usual way. An excellent continuous tone image is obtained.

This procedure is more advantageous than that in which the paper is bathed first in the developer solution and then in the silver salt solution.

What is claimed is:

1. In the process of developing a photograph from a relatively water-soluble silver salt at an invisible latent image formed by imagewise exposure of a photographic silver halide emulsion, the improvement according to which the silver salt is selected from the group consisting of a salt of phosphoric acid and a salt of an aliphatic carboxylic acid, the aliphatic chain of which is substituted with an organo thioether grouping and having a solubility in water at a pH between 1 and 7 of at least 0.2 g./l. silver in the form of salt.

2. In the process of developing a photograph from a relatively water-soluble silver salt at a silver image, the improvement according to which the silver salt is selected from the group consisting of a salt of phosphoric acid and a salt of an aliphatic carboxylic acid, the aliphatic chain of which is substituted with an organo thioether grouping and having a solubility in water at a pH between 1 and 7 of at least 0.2 g./l. silver in the form of salt.

3. In the process of developing a photograph from a relatively water-soluble silver salt by diffusion of said salt from a layer containing said salt and uniformly distributed development nuclei to a separate layer of imagewise distributed development nuclei, the improvement according to which the silver salt is selected from the group consisting of a salt of phosphoric acid and a salt of an aliphatic carboxylic acid, the aliphatic chain of which is substituted with an organo thioether grouping and having a solubility in water at a pH between 1 and 7 of at least 0.2 g./l. silver in the form of salt.

4. The combination of claim 3 in which the image is contained in an emulsion stratum that also contains the needed developer, and the developing is effected by moistening the stratum with water.

5. The combination of claim 1 in which the invisible latent image is formed by imagewise exposure and the developing is effected with a pyrazolidone-3 developer, a 3-aminopyrazoline developer, an aminopyrazolone developer,la hydroxytetronic acid or a salt of a reducing heavy meta 6. Th combination of claim 2, wherein the light-sensi tive silver salt is selected from the group consisting of a silver salt of an S-[phenyl]-thioglycollic acid, an S-[triazolyl] -thioglycollic acid, an S-[thiadiazolyl]thioglycollic acid and a bis-[B- (carboxymethylthio)-ethyl]-ether.

7. The combination of claim 3 in which the development is effected by aflixing to the face of the image a layer containing the relatively water-soluble silver salts dispersed in a permeable binder so that the salts diffuse out of the layer to the image nuclei and are there reduced, and the diffusion is more complete at the image nuclei than at other portions, leaving behind in the permeable 15 binder a negative imagewise distribution of the silver salts.

8. The combination of claim 7 in which the silver salts left behind in the permeable binder are developed to form a negative copy of the image.

9. The combination of claim 8 in which the afiixed layer is removed from the face of the image to provide a separate negative of the image.

10. The combination of claim 8 in which the permeable layer contains uniformly dispersed development nuclei and the development of the image copy and of the negative take place together.

11. The combination of claim 9 in which the image is in a water-dispersible stratum and the removal is effected by washing the image stratum away from the aflixed layer.

12. The combination of claim 1 in which the image is contained in an emulsion stratum that also contains the needed developer, and the developing is effected by moistening the stratum with water.

13. The combination of claim 2 in which the image is contained in an emulsion stratum that also contains the needed developer, and the developing is effected by moistening the stratum with water.

14. A dispersion in a water-permeable binder of a water-soluble silver salt of phosphoric acid or an organo thioether-substituted aliphatic carboxylic acid, the said silver salt has a solubility in water at a pH of between 1 and 7 at least 0.2 g./l. silver in the form of the silver salt, said dispersion also containing development nuclei for the salt, both the salt and the nuclei being uniformly dispersed in the binder.

15. The combination of claim 14 in which the dispersion is a thin layer on a support, the development nuclei are in a concentration corresponding to from about 1 to about milligrams of silver per square meter of the layer, and the salt is in a concentration of from about 0.1 to about 2.5 grams per square meter of the layer.

16. The combination of claim 14 in which the dispersion also contains aicd and has a pH no lower than about 1.

17. The combination of claim 14 in which the dispersion is a thin layer on a support, and is covered by a lightsensitive silver halide emulsion layer.

References Cited UNITED STATES PATENTS 1,414,309 4/1922 Schwartz 9695 3,042,514 7/1962 Roth 9629 3,261,685 7/1966 De Haes et al 9666 NORMAN G. TORCHIN, Primary Examiner A. T. SURO PICO, Assistant Examiner U.S. Cl. X.R. 9695 

